1. Field of the Invention
The present invention relates to a contra-angle or turbine head of a dental handpiece comprising a sleeve rotatably mounted in the head case and adapted to receive the plain shank of a dental tool, said sleeve being provided with claws movable in the radial direction between a position in which said shank is clamped by resilient means and a position in which said shank is released by an actuator operable against the force of said resilient means.
2. The Prior Art
Many systems have already been proposed with a view to hold the burrs within the contra-angle or turbine heads. In so-called low-speed contra-angle burrs the standardized burrs are provided with a shank having a diameter of 2.35 mm, a circular groove and a flat face to facilitate the holding of the tool in position. On the other hand, so-called high-speed contra-angles and turbines use burrs having a smooth shank 1.6 mm in diameter.
Holding these burrs in position is a difficult problem, for relatively ample tolerances are generally admitted for the shank diameter. Therefore, the clamping means should be capable of exerting a considerable pressure on the shanks so that the latter be firmly held in position, even when their diameter has its smallest tolerance.
According to a relatively old French Pat. No. 1,255,386, it is known to use a clamping jaw consisting of at least two semi-cylindrical, slightly curved shells rigidly coupled to a small bar parallel to the shell generatrices, the shank of the tool being held simply by frictional contact between said shells.